This invention relates to a multitubular heat exchanger mainly used in thermal and nuclear power plants.
Heat exchangers of this type of the prior art generally comprise a shell, a heating medium inlet formed in the shell, a plurality of tube bundles located within the shell and including a large number of U-shaped heat transfer tubes for permitting a medium to be heated to flow therethrough so that heat exchange may take place between the medium to be heated and a heating medium, an inlet for the medium to be heated and an outlet for the heated medium formed in the shell at one end portion thereof and each communicating with the U-shaped heat transfer tubes at one end portion thereof, and a vent tube interposed between the tube bundles and arranged in the longitudinal direction of the shell for removing noncondensable gas from the interior of the shell. In the heat exchangers constructed as aforesaid, the ratio of the amount of heat exchanged in the tube bundle near the inlet for the medium to be heated to the amount of heat exchanged in the tube bundle near the heated medium outlet has hitherto been 15:1, and this has caused the terminal ends of streams of the heating medium to be concentrated in the middle portion of the tube bundle near the inlet for the medium to be heated. The result of this has been that a heating medium and noncondensable gas stagnating zone is created in this portion, so that it has been impossible to remove noncondensable gas satisfactorily through the vent tube interposed between the tube bundles located near the inlet for the medium to be heated and the tube bundle located near the heated medium outlet. Thus heat exchangers of this type of the prior art have had the disadvantage of the heat transfer tubes corroding in the heating medium and noncondensable gas stagnating zone.